Manufacturers of electronic components use a variety of fabrication techniques to produce semiconductor devices. One technique that has many applications (e.g., deposition, etching, cleaning, and annealing) is known as "plasma-assisted" or "plasma-enhanced" processing. Plasma-enhanced processing is a dry processing technique in which a substantially ionized gas, usually produced by high-frequency electrical discharge, generates active metastable neutral and ionic species that chemically react to deposit thin material layers on or to etch materials from semiconductor substrates in a fabrication reactor.
Various applications for plasma-enhanced processing in semiconductor manufacturing include high-rate reactive-ion etching (RIE) of thin films of polysilicon, metals, oxides, and polycides; dry development of exposed and silylated photoresist layers; plasma-enhanced chemical-vapor deposition (PECVD) of dielectrics, aluminum, copper, and other materials; planarized interlevel dielectric formation, including procedures such as biased sputtering; and low-temperature epitaxial semiconductor growth processes.
Plasma-enhanced processes may use remotely-generated or locally-generated plasmas. Remotely-generated plasma is a plasma that a plasma-generating device produces external to a fabrication reactor. The plasma is guided into the main process chamber and there interacts with the semiconductor wafer for various desired fabrication processes. Locally-generated plasma is a plasma that a plasma-generating charged electrode forms within the process chamber and around the semiconductor wafer from suitable process gases. Conventional plasma processing reactors for etch and deposition applications usually employ 13.56 MHz plasmas, 2.5 GHz remote plasmas, or a combination of these plasmas. In conventional systems, a plasma-generating radio-frequency power source connects electrically to a conductive wafer holding device known as a wafer susceptor or chuck. The radio-frequency power causes the chuck and wafer to produce a radio-frequency plasma discharge proximate the wafer surface. The plasma medium interacts with the semiconductor wafer surface and drives a desired fabrication process such as etch or deposition.
Opposite and parallel to the wafer and chuck in these systems is a showerhead assembly for injecting the plasma-generating gas or gas mixtures into the process chamber. This is known as a parallel-plate configuration due the parallel surfaces of the chuck and showerhead. Typically, the showerhead connects to an electrical ground. In some designs, however, the showerhead assembly may connect to the plasma-generating radio-frequency power source, while the chuck and semiconductor wafer connect to an electrical ground. Still other configurations may use a combination of locally-generated plasma and remotely-generated plasma. In all of these known configurations, various limitations exist which contains the plasma process application domain.
Limitations associated with using only two parallel plates include inefficient in-situ chamber cleaning and less than desirable process control flexibility. In particular, the conventional parallel-plate configuration does not provide adequate control or adjustment over deposited plasma process uniformity. Moreover, there is no independent control over deposited film stress, deposition rate, and deposition uniformity. For example, a change in a process parameter to reduce film stress may adversely affect deposition rate, and vice versa. Further, no independent control over etch rate, selectivity, or anisotropy in plasma-enhanced etch and RIE processes occurs in these types of systems.
Consequently, there is a need for a semiconductor wafer fabrication process that overcomes the limitations of known systems to permit efficient in-situ chamber cleaning while providing necessary control over plasma-enhanced fabrication processes.
There is a need for a method and apparatus for plasma-enhanced semiconductor device fabrication that offers improved control over known methods and apparatuses. In particular, there is a need for a plasma-enhanced device fabrication method and system that improves the control and adjustment of semiconductor wafer plasma processing uniformity.
There is a need for a semiconductor wafer fabrication method and apparatus that offers flexible control over film stress, deposition rate, and deposition uniformity in plasma-enhanced deposition applications.
Furthermore, there is a need for a method and system that permits flexible control over semiconductor wafer etch rate, selectivity, and anisotropy in plasma-enhanced RIE processes.